Evidence suggests a critical involvement of the dopaminergic mesocorticolimbic system in positive reinforcement. A frequently employed model used to study reward behavior is electrical brain stimulation reward (BSR) in which animals perform a task in order to receive electrical stimulation to a discrete brain area. The deoxyglucose method is being used to study alterations in brain metabolic activity during BSR and following the administration of drugs with euphorogenic properties. The deoxyglucose method has been used to identify the sites of action of the reward-enhancing effects of cocaine and morphine in BSR paradigms. These data demonstrate that cocaine and morphine may exert their euphorogenic effects in this paradigm through actions at the same site, the olfactory tubercle. The long term consequences of the administration of drugs classified as abused substances have also been studied with the deoxyglucose method. In these studies, reductions in glucose utilization in the dorsal and ventral striatum were evident after chronic methamphetamine treatment. Immunocytohistochemical studies were carried out to measure expression of c-Fos protein which is thought to act as a genetic transactivator regulating gene expression. Increased presence of Fos was observed in the striatum of rats treated with cocaine, suggesting a possible mechanism for the long term effects of cocaine.